Description:(Adapted from the application) Phosphorylation of smooth muscle myosin (SMM) and nonmuscle myosin II is required to activate cellular functions. A single serine in the regulatory light chain (RLC) of each of the two "head" domains of myosin is phosphorylated by a calcium-activated kinase. Current knowledge suggests that this regulatory effect is mediated through large conformational changes in myosin structure. Dr. Cremo's long-term goal is to determine the structural basis of the phosphorylation-dependent regulatory mechanism. Dr. Cremo hypothesizes that a specific interaction between the two heads is favored in the unphosphorylated "off" or down-regulated state. A prediction of the hypothesis is that the rod domain near the heads is altered by phosphorylation, thus assisting in breaking the interaction between the heads. Dr. Cremo now extends this hypothesis to the idea that the interaction between the two heads is not symmetrical, based upon recent findings from her laboratory. She presents a detailed "structural hypothesis" for how phosphorylation of the RLC controls the head-head interactions. She will also test the hypothesis proposed by others that interactions between the two catalytic domains, controlled by regulatory domain interactions, explain the down-regulated kinetics of the unphosphorylated state. These experiments should answer the question "How does phosphorylation of two residues at the head-tail junction alter the structure of two ATP binding sites 15 nm away?" The Specific Aims are: (1) Obtain secondary and tertiary structural data about the RLC of myosin and construct a 3-dimensional model to address the molecular mechanism of phosphorylation-dependent regulation. (2) Obtain initial quaternary structural data concerning the inter-head interactions between the two ELC (essential light chain), between the ELC and the heavy chain, and between the two heavy chains. (3) Determine which portions of one head must be present to down-regulate the partner head. (4) Obtain secondary and tertiary structural data about the rod region of myosin near the heads and construct a three-dimensional model to address the molecular mechanism of phosphorylation-dependent regulation.